1. Technical Field
The present invention relates to an illuminating device and a projector.
2. Related Art
In recent years, high-luminance and compact projector are needed. In order to meet the needs, a projector (so-called two-light-type projector) using an illuminating device having a pair of light source units which are arranged such that the emission directions of illumination beams become mutually different directions, and two reflecting elements which reflect the illumination beams emitted from one light source unit, among the illumination beams emitted from the pair of light source units, towards the same direction as the emission direction of the illumination beams emitted from the other light source unit is suggested (for example, refer to JP-A-2005-346109).
According to such a two-light-type projector in the related art, since the pair of light source units are used, a high-luminance projector can be configured. In addition, in an illuminating device (hereinafter referred to as “illuminating device in the related art”) used for the two-light-type projector in the related art, only the illumination beams (hereinafter referred to as “central illumination beams”) emitted from a region within a certain range including the optical axis of a light source unit, among the illumination beams emitted from the light source unit, are utilized as illumination light, and the illumination beams (hereinafter referred to as “peripheral illumination beams”) emitted from a region out of the certain range are not utilized as illumination light. However, the in-plane light intensity distribution of the illumination beams emitted from the light source unit becomes a distribution having a characteristic curve showing a steep peak in the optical axis of the light source unit and in the vicinity thereof and showing a sharp decline as it goes away from the optical axis of the light source unit. Therefore, even if the peripheral illumination beams in the light source unit are not utilized as illumination light, a sufficiently high-luminance projector is obtained.
Moreover, according to the two-light-type projector in the related art, the pair of light source units are not arranged in parallel such that all the emission directions of illumination beams become the same direction, but the pair of light source units are arranged such that the emission directions of illumination beams become mutually different directions and the emission directions of the illumination beams emitted from the pair of light source units are aligned with one direction by using two reflecting elements. Therefore, a high-luminance and compact projector can be configured.
Meanwhile, in the two-light-type projector in the related art, there is a demand to further enhance the light utilization efficiency in an illuminating device. If the light utilization efficiency in an illuminating device can be enhanced further, not only the luminance of a projector can be increased, but also the stray light level in an illuminating device is reduced so that the image quality of a projection image can be improved. Moreover, generation of unnecessary heat resulting from stray light, etc. can be suppressed, and the heat-radiating structure can also be simplified.